There is a new pull request by AN3223 against master on the void-packages repository

https://github.com/AN3223/void-packages openvpn_service
https://github.com/void-linux/void-packages/pull/17906

openvpn: Added a service for running as a client
Systemd service for reference: https://github.com/OpenVPN/openvpn/blob/master/distro/systemd/openvpn-client%40.service.in

A patch file from https://github.com/void-linux/void-packages/pull/17906.patch is attached